(1) Field of the Invention
This invention relates to a metallic slug for expulsion from an industrial ballistic tool. More particularly, it relates to a cost-efficient, environmentally friendly, frangible slug.
(2) Description of the Related Art
Industrial ballistic tools are used in a variety of applications. One common application is the in situ cleaning of kilns, for which the tools are commonly identified as kiln guns. Additional applications lie in the tapping and cleaning of furnaces, the cleaning of copper smelters, the cleaning and clearing of silos, the cleaning of boilers, and the like.
By way of example, rotary kilns, which are used to calcine cement and lime, are typically 3 to 7 meters in diameter and 30 to 150 meters long. Calcining takes place at elevated temperatures, typically in the range of 1100° C. to 1500° C. During the calcining process, because of many processing variables, the product may adhere to the sidewall of the kiln forming a clinker, ring or dam. If this adherent obstruction is not removed, additional product will accumulate, reducing or stopping throughput. Removal of the obstruction is necessary.
It is not economically feasible to stop the kiln to remove the obstruction. Also, considering that the ring may form 5 to 10 meters from the end of the kiln, it is not safe or efficient for an operator to attempt to manually remove the obstruction with a long pole or by like methods. Thus many users of rotary kilns utilize industrial ballistic tools. A tool operator will position the tool in a kiln port and then fire metallic projectiles at the obstruction. Impact of the projectiles with the obstruction removes the obstruction from the sidewall of the kiln.
The metallic projectiles are usually formed from lead, a dense material with a relatively low vaporization (boiling) temperature of 1750° C. The lead projectiles knock clinkers from the kiln sidewall and then fall into the kiln and may be vaporized.
Industrial ballistic tools are also utilized by manufacturers of steel, ferrosilicon and other materials. Prior to casting these metals, molten metal is typically contained within an electric furnace sealed by a carbon or clay base plug. Since the molten metal is at a temperature in excess of 2500° C., manual removal of the plug is not feasible. One way that the plug may be removed is with an industrial ballistic tool. A metallic projectile is fired from the industrial ballistic tool to break open the plug, starting the flow of molten metal. To prevent contamination of the metal, the projectile typically is formed of a material such as lead that will vaporize on contact with the molten metal after rupturing the plug.
Due to environmental concerns, lead is being phased out as a projectile material for use with industrial ballistic tools. By way of comparison, the use of an exemplary 85 grain lead slug in a kiln or furnace application would introduce up to 85 grams of lead into the atmosphere. Prior to its removal from the U.S. market, a gallon (3.79 l) of leaded gasoline would contain approximately 0.1 grams of lead. Thus each lead slug represents the equivalent of about 3,000 liters (850 gallons) of such leaded gasoline. With the necessity to use many hundreds of slugs per day in certain kiln applications, the amount of lead involved can be significant.
Several substitutes have, to date, proven unsatisfactory. Iron and steel are much harder than lead, causing cast or forged iron or steel-based projectiles to be prone to excessive penetration and ricochet, potentially damaging the kiln and/or injuring the operator. U.S. Pat. No. 3,232,233 of Arthur Singleton discloses iron-based industrial slugs. The slugs are compacted and then sintered at a high temperature. An exemplary such slug is pressed at 414 MPa (30 tons per square inch (tsi) (60,000 psi)) and sintered at a temperature of 982° C. (1800° F.) for a minimum of 45 minutes. To facilitate fragmentation of the slug, it is optionally provided with a compartment or “cavity” to provide a rupture plane. The provision of such cavities adds additional manufacturing complexities and reduces the mass associated with a given overall size or envelope of a projectile.
Zinc and zinc alloys have also been utilized as lead substitutes. Their relatively low density may make them disadvantageous for certain uses. A ballistically stabilized zinc-based projectile is described in U.S. Pat. No. 5,824,944 of Jack D. Dippold et al.
Due to the phasing out of lead-based projectiles, there remains a need for a non-lead-based metallic projectile for use with industrial ballistic tools that does not suffer from the above-stated disadvantages.
Accordingly, it is an object of the invention to provide metallic projectiles for expulsion from an industrial ballistic tool effective to remove clinkers from kilns and/or carbon or clay plugs from electric furnaces.